Background: Fukushima Daiichi Nuclear Power Plant began to release radioactive substance after the earthquake on March 11, 2011, which included radioactive iodine and cesium. Therefore, incidence of thyroid cancer among childhood in the area has been a public health concern. The committee of health control examination in Fukushima Prefecture planned thyroid cancer screening for all children aged 18 years or younger every 3 years. The results of the screening have been released every 3 months. The screening was undergone at the nearest areas from the power plant in the first year (until March 31th, 2012), then at the moderately near area including Fukushima City in the second year (until March 31th, 2013). We present our findings based on the data until June 5th, 2013. Aim: To estimate childhood thyroid cancer incidence rate ratio in Fukushima, compared with age, sex-specific incidence estimates of thyroid cancer (1975-2008) from the Center for Cancer Control and Information Services, National Cancer Center, Japan. Poisson distribution was employed to estimate 95% confidence intervals. Results: From the nearest area group (mostly within 50km from the power plant: 40,764 examinees), 205 cases were suspected by ultrasound imaging, 166 (81.0%) were undergone on the 2nd examination, then, 11 thyroid cancer cases were identified by cytology, of which 7 cases have been operated and confirmed. Mean age of the cancer cases in the nearest area was 17.3 (range 13-19) years old, and mean diameter 14.1 mm (range 6.0-33.0mm). From 46,367 examinees of Fukushima City (50-80 km from the power plant), 263 cases were suspected by ultrasound imaging, 228 (86.7%) were undergone on the 2nd examination, then, 9 thyroid cancer cases were identified by cytology.?Assuming two years for duration on detectable level of cytology until clinical level, incidence rate ratio was 26.98 (95% confidence interval, 14.12-48.61) in the nearest area, and in Fukushima city, it was 19.41 (95% confidence interval,?9.62-37.31), compared with the Japanese mean annual incidence among those aged 15-19 years from 1975 to 2008 (i.e., 5 per 1,000,000).

Conclusions
: Although any screening effect may exist, excess incidence rate ratios were observed in both the nearest area and Fukushima City. Dose-response relationship by distance from the plant was indicated. Both further investigations and countermeasures against the suspected outbreak are necessary in Fukushima and the neighboring areas.

Tsuda and Yorifuji’s Research Office Department of Human Ecology, Okayama University Graduate School of Environmental and Life Science 3-1-1 Tsushima-naka, Kita-ku, Okayama, 700-8530, Japan